Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-12-18
2001-03-27
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S718000
Reexamination Certificate
active
06208151
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to measurement of electrical characteristics, and more particularly to an improved method and apparatus for measurement of selected electrical characteristics in integrated circuits and small scale semiconductor materials.
BACKGROUND OF THE INVENTION
As the size of semiconductor devices decreases, it becomes much more difficult to accurately measure the electrical characteristics of the devices. This is particularly true for very large scale integrated circuits fabricated on semiconductor wafers with very small spacing between components, especially those fabricated with low resistance metals and other types of electrically conducting materials. Currently, there are several methods and associated equipment for measuring electrical characteristics of complex transistor-size integrated circuits. These methods include scanning capacitance microscopy and the use of scanning tunneling microscopes (STM), as well as atomic force microscopes (AFM).
One method common to the art involves using a scanning probe connected to a voltmeter to measure the voltage drop across a sample of electrically conductive material attached to a current source. Accurate measurements are sometimes difficult to obtain with this method because the electric potential of the contact between the probe and the sample may vary with position and be large enough to affect the measurement.
In order to overcome problems associated with contact potential, a second type of measurement uses a voltmeter permanently affixed to opposite ends of the sample. An electron microscope may then be used as a current source and used to supply current to selected portions of the sample. While this method successfully overcomes the problems associated with the electric contact potential, it is also sometimes difficult to achieve accurate results. In order to use an electron microscope, the sample must be measured in a vacuum. Also, the available beam current is small in electron microscopes and this limits accuracy.
Many of the methods and equipment used for measuring electrical characteristics of integrated circuits at a microscopic level lack sufficient spatial resolution. It is difficult to conduct reliable measurements on microscopic devices or samples.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen in the art for an improved method for microscopic measurement of electrical characteristics. The present invention provides a method and apparatus for microscopic measurement of electrical characteristics that substantially eliminates or reduces problems associated with the prior methods for measurement of microscopic electrical characteristics.
In accordance with one aspect of the present invention, a method and apparatus for microscopic measurement of electrical characteristics may include a standard atomic force microscope (AFM). The AFM may have a small, pointed electrically conductive AFM tip attached to one end of a softly compliant AFM cantilever arm which includes an electrically conductive path to the tip. The other end of the cantilever arm may be attached to the top of a piezo-electric z-axis driver which will raise and lower the cantilever arm as the AFM tip is scanned across the surface of a sample. A piezo-electric X-Y scanstage may also be provided and connected to the z-axis driver. The X-Y scanstage is preferably capable of scanning the movement of the entire system including the z-axis driver, cantilever arm and AFM tip.
The AFM arm may be connected to a current source with one or more electrically conductive leads. The current source may also be connected to a sample. The AFM, leads and sample cooperate with each other to create a circuit for the flow of electricity from the current source through the sample. More specifically, a voltmeter may be connected to other points on the sample with electrically conductive leads. The voltage from this meter can be used with some measure of the electrical current to determine the microscopic electrical characteristics of the sample.
Technical advantages of the present invention include providing a more efficient method of measuring microscopic electric fields. By using an AFM to inject or supply current at selected locations in a sample and simultaneously measuring the voltage drop, electrical characteristics such as variations in resistance or conductivity throughout the sample may be accurately measured. Also, the present invention allows such measurements to be taken in a normal atmospheric environment (no vacuum required).
Further technical advantages of the present invention include providing a system of measurement of microscopic electrical characteristics utilizing currents larger than those commonly available in scanning electron microscopes. Also, methods and apparatus within teachings of the present invention allow accurate measurements of electrical characteristics to be conducted on a smaller scale and at a reduced cost in comparison with conventional microscopic electrical characteristic measurement methods.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims.
REFERENCES:
patent: 4178543 (1979-12-01), Wrinn et al.
patent: 4918377 (1990-04-01), Buehler et al.
patent: 5530372 (1996-06-01), Lee et al.
patent: 5723981 (1998-03-01), Hellemans et al.
Aton Thomas John
Files Leigh Ann
Brady III Wade James
Garner Jacqueline J.
Metjahic Safet
Nguyen Vincent Q.
Telecky , Jr. Frederick J.
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